1. Technical Field
The present invention relates in general to improved data storage systems and in particular to improved methods and systems for the location of synchronization characters within data stored within a data storage system. Still more particularly, the present invention relates to improved methods and systems for locating synchronization characters within data stored in a data storage system by predicting the occurrence of specific synchronization characters during selected periods of time.
2. Description of the Related Art
Modern data processing systems often use digital signal recording devices attached to host processors to record records as addressable units within magnetic tape storage systems.
Examples of systems which may be utilized to record records within a magnetic tape storage system are disclosed within Milligan et al., U.S. Pat. No. 4,393,445; Milligan et al., U.S. Pat. No. 4,435,762; Videki II, U.S. Pat. No. 4,471,457; Cole et al., U.S. Pat. No. 4,603,382; Bauer et al., U.S. Pat. No. 4,423,480; and Fry et al., U.S. Pat. No. 4,403,286. Each of the aforementioned patents discloses a magnetic tape storage system which may be advantageously employed in carrying out the method and system of the present invention.
In such data storage systems, it is practically a necessity that each track of data within the recording medium include multiple synchronization characters. Such synchronization characters are necessary so that the data may be considered self-synchronizing. Without such self-synchronizing, data may not be successfully recovered.
In modern data storage systems data is typically written to multiple tracks simultaneously. When such multiple track recording is utilized it is possible to determine various necessary parameters which may affect data recovery, even though individual track data within a group of multiple tracks may be lost. One such parameter is the location of the end of a particular block of data. It is imperative to accurately identify the end of a block of data in order to prevent errors which may occur due to overwriting data when additional data is appended to a record.
Systems which have been proposed to detect the end of a data block more reliably typically use a group of diverse synchronization characters which are positioned in a unique order within a data block, such that the end of a data block may be successfully located even though multiple tracks within a multiple track group have lost synchronization, the detection of such diverse synchronization characters presents a problem for individual tracks within a multiple track recording system, since a track may lose synchronization and thus, may not know what particular synchronization mark to expect. If an individual track within a multiple track recording system does not know which synchronization character to expect that track may never synchronize or may synchronize at the wrong point. If a large enough number of tracks within a multiple track system lose synchronization, the ability of known error correction circuitry to correct such problems is soon exceeded and the data cannot therefore be recovered.
It should therefore be obvious that a need exists for a method and system whereby the location and identification of unique synchronization characters within a data block may be accomplished. Additionally, such a system should be sufficiently robust such that variations in tape speed and occasional missed synchronization marks will not result in a loss of synchronization for an individual track.